1. Field of the Invention
The present invention relates to internal combustion engines, and in particular to two stroke engines.
2. Description of the Related Art
Conventional two stoke engines feed a fuel-air mixture into a crankcase that is below a piston in a cylinder. From the crankcase, the fuel-air mixture is then directed into a combustion chamber by pressure generated by the piston travelling into the crankcase. This two stroke engine has the disadvantage that oil from the crankcase, used for lubrication, is undesirably mixed with the fuel-air mixture, which is then combusted in the combustion chamber, producing unwanted pollutants and reducing power output.
In U.S. Pat. No. 4,993,372 issued Feb. 19, 1991 to Mott et al., there is shown a two stroke internal combustion engine that has in the cylinder wall an inlet port to which fresh air is supplied under pressure, the inlet port being covered and exposed by the piston during reciprocation thereof in the cylinder. This engine makes use of an exhaust valve to release combusted gases. Since the exhaust is under high pressure, the use of a valve for the exhaust reduces the reliability of the engine.
In U.S. Pat. No. 4,719,880 issued Jan. 19, 1988 to Schlunke et al., there is disclosed a direct injected two stroke cycle internal combustion engine having a cylinder, a cylinder head at one end of the cylinder, a piston mounted for reciprocation in the cylinder, and an inlet port and an exhaust port in the wall of the cylinder at substantially diametrically opposite locations in the cylinder. This internal combustion engine does not make use of a forced air induction component.
In another type of two stroke engine, a fan blows a fresh gas and air mixture into a cylinder when a piston uncovers an inlet port so that any residual exhaust is flushed out through an exhaust port. This type of two stroke engine suffers from the disadvantage of having unburnt fuel escape through the exhaust port while the fan blows the fuel-air mixture into the cylinder.
In theory two-stroke engines should have twice the power compared to four-stroke engines with the same displacement, because two-stroke engines have twice the number of power strokes. Conventional two-stroke engines are known to be less complex, compact, light, cheaper to manufacture and to maintain, whereas four-stroke engines are proven to be reliable and clean burning. The invention of direct injection has improved fuel efficiency and reduced emissions in two-stroke engines.
It is an object of the present invention to combine the advantages of 2-stroke engines, namely the advantages mentioned above, with the reliability of four-stroke engines by bringing together the concepts of direction injection and a fan-scavenged two-stroke engine.